A wide variety of technologies are known and have been implemented for identifying a desired position on a display screen of a processor-based system. For a CRT display, light pens in communication with the host processor sense the instant of time when a raster scanning beam stimulates a pixel element and so can identify the location to which the pen is pointing. As processing systems have tended to use active matrix liquid crystal displays for their size and power consumption advantages, other types of technologies have been employed that use a locator device separate from the display. In particular, tablets, beams or films are supplementally associated with the basic display. But they have to be calibrated to the display to identify a desired position. Touch screens, where a finger is employed as the pen, have the lowest resolution but are effective in identifying relatively large areas on the screen. Typically, a light beam grid passes over the display screen from top to bottom and from right to left so that when a series of the beams are broken by a finger, the broken beams identify the finger position in the x-y beam grid. Another low resolution system involves opposed films sandwiching a non-conductive layer. Each of the films include a series of signal lines in an x- and y- direction, respectively. When one presses on the film, the films touch to cause a short between the signals lines at that position, essentially closing a switch which can identify the touch position. Both of the foregoing systems are referred to as "touch screens" and are of the lowest resolution type position detection systems.
"Pen-on-screen" systems have improved resolution over touch screens and typically employ a tether line between the pen and a host processor. A tablet is associated with the display screen which has a plurality of electrical contacts about its periphery. When the pen makes a contact with the tablet, the host processor can measure particular resistances between the pen and each of the contacts, and from such resistances can determine the location where the pen is touching the screen. A similar system can be employed with variable capacitances between the touching pen and the peripheral sensors. In this latter system the pen is employed as a contact to generate an electrical signal which is measured by each of the contacts for calculating a relative position. More complex systems have employed an LRC circuit in the pen itself with a series of antennas about the periphery of the tablet, wherein a radio frequency pulse generated by the antennas is sensed by the LRC circuit. The detected resonance in the pen will vary with respect to position on the tablet so that the processor can localize pen position.
A common problem with all of the aforementioned systems is that they employ a separate device which must be calibrated to the actual display screen with which it is associated. The calibration process involves placing an image on the display screen and touching the tablet in different spots until the tablet is calibrated to match the display screen. Such calibration systems have been fairly successful for low resolution displays, where the resolution has approached one-two hundredth of an inch (1/200").
Display devices have advanced to have a resolution beyond the resolution of the above-referenced prior known position detection systems. A pixel on a currently available high resolution display (the dpiX 7 Million Pixel ALMCD) is approximately ninety microns (90.mu.) across--one-two hundred eighty second of an inch (1/282"). The prior known systems can not localize relative position down to a particular pixel of this size. Even if the technology were improved to have matching resolution capabilities, the calibration problems would continue to increase so that the systems themselves would have limited economic and practical value.
The present invention contemplates a new and improved system which overcome all the above-referred to problems, and others, to provide a new position identification and cursor locating system which is practical in application, simple and economical to manufacture, readily adaptable to a plurality of display types, and which avoids the necessity of maintenance of close calibration between a position location tablet and the actual display screen.